This disclosure relates to a lubrication system for gas turbine engines and more particularly to a configuration for overcoming oil coking in the lubrication system.
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustor section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines. High and low spools or shafts respectively support the high pressure and low pressure turbines and compressors.
The engine has bearings that support the high and low shafts. The bearings are typically housed in bearing compartments that are connected to a lubrication system. The lubrication system provides lubricant, such as oil, to the bearing compartment through a supply line to lubricate and cool the bearings. The lubrication system also recovers the oil from the bearing compartment through a scavenge line and sends the oil through a filter and heat exchanger before cycling the oil back to the bearing compartment.
At shutdown of the gas turbine engine, the lubrication system ceases to circulate oil to the bearing compartment and the oil, now without pumping pressure, drains out of both the supply line and the scavenge line and back to a sump or low point in the lubrication system. With the lubrication system inactive and no longer dissipating heat from the bearing compartment, heat produced by the gas turbine engine just prior to shutdown can “soak” into both the bearing compartment and the supply and scavenge lines and can excessively elevate the temperature of these engine components. The elevated temperatures caused by the heat soak back can cause oil mist or film located in the supply and scavenge lines to react with air and form coke deposits on the inside surfaces of the supply and scavenge lines. Over time, these coke deposits can accumulate and clog the tubes preventing oil from flowing to the bearing compartment. Without an adequate supply of oil, the bearings in the bearing compartment can fail and result in engine-wide failure of the gas turbine engine.